Balance device for parallel drafting machines



July 21, 1970 TAMIC SIHIMIZVU BALANCE DEVICE FOR PARALLEL DRAFTING MACHINES Filed June 19, 1968 .4 Sheets-Sheet 1 TORQUE CURVE m T N I C E .0 M y n\ E S U .u v mu o O E 9. m m N O ll M G m & m NU, ME A o m N :m E I' O MUEOL OZEnW TAMIO $HIMIZU July 21, 1970 TAMIQ sHuvuzu. ,5

BALANCE DEVICE FOR PARALLEL DRAFTING MACHINES Filed June 19. 1968- .4 Sheets-Sheet 2 IN-VEN TOR.

TAM/0. SHIMIZU' July 21, 1970 TAMIO SHIMIZU 3,521,363

BALANCE DEVICE FOR PARALLEL DRAFTING MACHINES .4 Sheets-Sheet 3 Filed JIme 19. 1968 11V VEN TOR. TAMIO SHIMIZU July 21, 1970 mm sam'lzu 3, ,363

BALANCE DEVIOEFOR PARALLEL DRAFTING MACHINES Filed June 19,1968 .4 Sheefgs-Sheet m VEX T0 12. TAMIO SHIMIZU United States Patent 3,521,363 BALANCE DEVICE FOR PARALLEL DRAFTING MACHINES Tamio Shimizu, Tokyo, Japan, assignor to Muto Kogyo Kabushiki Kaisha, Tokyo, Japan Filed June 19, 1968, Ser. No. 738,157 Claims priority, application Japan, July 11, 1967, 42/598,955; July 26, 1967, 42/41,15s Int. Cl. B43i 13/02 U.S. C]. 3379 4 Claims ABSTRACT OF THE DISCLOSURE The balance device for parallel motion drafting machines in accordance with the present invention comprises an arm pivotally mounted on a pin and having a stepped extension at its one side, and a spring having an end slidably mounted on and along the stepped extension of the arm by means of a roller secured to the end and other end pivotally anchored to a support means such as a plate or bracket. The balance device is housed in a pulley guard or enclosure associated with a clamping means by which a parallel motion machine is rigidly secured to a drawing board balances the drafting machine on the drawing board tilted at the selected positions on angles wtih respect to a vertical plane.

BACKGROUND OF THE INVENTION This invention relates to a balance device for parallel motion drafting machines, and especially to a balance device comprising a rockable arm having a stepped extension at its one side and a sring having an end on which a roller is mounted to slide along the stepped extension, and other end pivotally anchored. With the arrangement of these members, the balance device may be constructed in a small size or compact enough to be housed in a pulley guard or enclosure associated with a clamping means which is a part of the balance device.

The balance device generally used in the previous parallel motion drafting machines is comprised of a relatively massive balance weight carred by a bar which extends out of a drawing board, and rocks relative to the drawing board when the latter is tilted. Consequently the balance device of such a type is in some cases inconvenient for drawing operations.

An object of the invention is to provide a balance device capable of obviating the ditficulty encountered in the drawing operation in the previous parallel motion drafting machine with the balance weight, and further to provide a compact and light balance device.

DESCRIPTION OF THE DRAWINGS FIGS. 1 to 6 are schematic diagrams for showing the principle of balance action applied to the balance device for a parallel motion drafting machine in accordance with the present invention, in which figures the variation of torque of a weight moving on a circle with respect to the center of the circle, a spring force to be balanced with the torque of the weight and the characteristics of a coiled spring when it is elongated or stretched.

FIG. 7 shows the outline of the construction of a parallel motion drafting machine.

FIG. 8 is a vertical sectional view showing a pulley guard housing a balance device in accordance with the present invention.

FIG. 9 is a vertical sectional view taken on the line different from that in FIG. 8 and showing the arrangement of a first and second supporting arms of a parallel motion drafting machine.

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FIG. 10 is a horizontal sectional view taken along line XX in FIG. 8 and looked in the direction of the arrows.

The principle of balance action will be explained with reference to FIGS. 1 and 3. Reference figure W designates a weight carried on the outer end of a lever 1 that has length L and rotates about a center 0 at which the inner end of the lever 1 is pivoted. Then the trace of moving weight W is a circle ABCD. The torque of the movable weight W with respect to the center 0 may be expressed by the formula W-R or W-L cos 0 wherein R is an arm and 0 is a variable angle between the lever 1 and a horizontal axis BD, and also may be expressed by a graph as illustrated in FIG. 2. The torque of the weight W may be usually balanced with a force such as exerted by the elongation of a spring as arranged in such a way as illustrated in FIG. 3. In FIG. 3, reference numeral 2 designates a rotatably supported disc at its own center 0 and having a circumference ABCD and a pin 20 positioned on the circumference ABCD. Now let us assume that a weight or load similar to the weight W is applied to the pin 20, the rotation of the disc 2 may be regarded to correspond to the circular movement of the weight W and the torque applied on the disc 2 by the load applied on the pin 20 also may be treated similarly to that in FIG. I. A link 3 is pivotally connected at its end to the pin 20 and its opposite end is pivotally connected to one end of a rockable lever 4. The rockable lever 4 has a fulcrum 40 for rocking motion, and biased with a spring 5 located at the opposite side from the link 3 and slidably carried thereon by means of a roller 6. The load on the pin 20 is transmitted through the lever 4 to the pivotal joint of the link 3 and rockable lever 4, and the spring force of the spring 5 is also transmitted through the rockable lever 4 to the same pivotal joint and the two forces are balanced thereat. The pivotal joint of the link 3 and rockable lever 4 is provided to position at Q on line e passing through the center 0 of the rotatable disc 2, consequently the torque of the load on the pin 20, even if the pin 20 is located on an arc ABC or ADC, may be balanced with the spring 5 in the same way, because the variation of the torque of the load on pin moving along the arc ABC is the same as that along the arc ADC as shown in FIG. 2. Therefore, the balance of torque will be explained with reference to the arc ABC.

When the pin 20 positions at P and P which are spaced from the vertical axis ef in an equal horizontal distance, the torques of the load at P and P with respect to the center 0, which load acts vertically downwards, viz. in the direction parallel to the axis of, are equal to each other as seen from the graph in FIG. 2, but if such loads are balanced through the link 3 by the rockable lever 4 biased with the spring 5, the torques of the load acting in the direction parallel to the longitudinal axis of the link 3 at P and P with respect to the center 0 or the fulcrum 40 differ from each other, because their respective arms of moment differ from each. It is here noted that the fulcrum point 40 may be regarded as a datum point instead of the center 0. When the pin 20 moves from P to P the pivotal joint of the link 3 and rockable lever 4 shifts from Q to Q below Q and adjacent to the axis of, by selecting the lengths of the link 3 and the left portion of the rockable lever 4 from the fulcrum 40. Then the torque of the load on the pin 20 at P with respect to the center 0 chosen for convenience for illustration is W (load) 0R (arm) that is greater than the torque W (load) OR (arm) at P To balance these torques, the spring force of the spring -5 or the torque thereof with respect to the fulcrum 40 should be varied to accord with the variation of the torque of the load. The spring force of the spring 5 developed by its elongation and required to balance the torque of the load on pin 20 moving along the arc ABC is graphed in FIG. 4. It is noted that in response to the movement of the pin 20 the end of the spring 5 provided with the roller 6 moves toward the fulcrum 40. Line AB is the spring force required to balance the load on the pin 20 moving from A to B (90 and line BC is the spring force required when the pin 20 situates on the are BC. As is seen from the graph including the lines AB and BC, if a spring having the characteristic of the spring force designated by a line BC is used for balancing the torque of the load on the pin 20- situated on the arc, its gradient is expressed by a line CBDO, and the spring force on the line ED is less than that on a line AB which is required for balancing of the load, thus the pin 20 will move freely downward along the arc AB. On the contrary, in case other spring having the characteristic of the spring force designated by a line AB, its gradient is expressed by a line EBA and the spring force in the range of the line BB is less than the required spring force expressed by the line BC. Besides, the initial elongation of the spring given to the spring, which is expressed here by the length 0 A, is greater than that expressed by the length 0 D. The greater initial elongation of the spring makes the balance device greater in size and is objectionable. The use of a spring having the characteristic of the spring force expressed by dash lines AC also is objectionable because of the initial elongation of the spring being great.

The most desirable spring for balance is to use the spring having the characteristic of the line BC and provide means which make the same to follow the characteristic of line AB after the pin 20 passes through the point B.

The inventor found that such a desirable spring may be obtained by providing a step 7 in the straight rockable lever 4 in FIG. 3 and forming it to have a straight portion 8, step 7 and another straight portion 4 as illustrated in FIG. 5. In this arrangement, if the pin 20 moves from the point A to the point B, during its movement, the spring 5 continues to swing to the left because its one end is fixedly anchored and other end slides on the rockable arm portion 4 by means of the roller 6, and is stretched. When the movement of the pin is stopped, the movement of the spring 5 also stops at a position at which the spring force of the stretched spring 5 balances with the load on the pin 20, viz. the longitudinal axis of the spring 5 is normal to the lever portion 4, in other words, the torque of the stretched spring force with respect to the fulcrum or pivotal pin balances with the torque of the load on the pin 20 with respect to the same fulcrum 40.

When the pin 20 moves through the point B to point C, the swing movement of the spring 5 is stopped by the shoulder of the step 7 as shown by dash lines in FIG. 5, and the distance between the roller 6 and fulcrum 40 is kept at a constant during the further movement of the pin 20 along the arc BC and the balance of the load on the pin 20 is efiected with the spring force of the stretched and stopped spring 5. For this reason the spring having the characteristic of the line BC may be applied to the balance of the load moving along the whole are ABC.

In FIG. 6 there is diagrammatically illustrated a combined two balance means wherein one balance means is cooperatively associated with the other means. The balance means of this type may be advantageously applied to a parallel motion drafting machine hereinafter described.

Now, a preferable embodiment of a balance device based on the principle of balance hereinbefore described and adapted to a parallel motion drafting machine as outlined in FIG. 7 will be explained -with reference to FIGS. 8 to 10. The parallel motion drafting machine illustrated in FIG. 7 comprises a first supporting arm 101, a second supporting arm 104, a clamping means 102 located at the outer end of the first support arm 101, a square scale 147 located at the outer end of the second supporting arm 104, and a series of pulley enclosures or guards including a first pulley guard 111, a second pulley guard 110, a third pulley guard 141, and a fourth guard 160. The first pulley guard 111 carries within it a joint assembly of a pin 120 and a tubular stub shaft 121 as illustrated in FIG. 8; the second pulley guard is coaxially disposed with and above the third pulley guard 141 and they commonly carry within them a joint assembly of a pin 142' and a tubular stub shaft 142 as illustrated in FIG. 9; and the fourth pulley guard 160 also carries within it a joint assembly not shown, but similar to the joint assembly shown in FIG. 8 for pivotally connecting the second pulley guard 104 and the square scale 147.

Referring to FIG. 8 showing the first pulley guard 111 and the clamping means 102 associated therewith, the first supporting arm 101 is rigidly secured to the first pulley guard 111, and the first pulley guard 111 is rotatably mounted through bearing bearings 122 on a tubular stub shaft 121 which is rigidly secured to the body of the clamping means 102. Rotatably fitted in the tubular stub shaft 121 is a pin which is rigidly connected to a pulley 146 driven by rope-s 145 training around there. The movement of the rope 145 will be hereinafter explained. Rigidly mounted on the bottom of the first pulley guard 111 is a gear 112. The gear 112 (FIG. 10) engages a gear 113 secured to the body of the clamping device 102, and the gear 113 includes an eccentrically disposed pivot pin 15 on which a link 114 is pivotally supported. The opposite end of the link 114 is pivotally connected through a pivot pin 118 to one end of a rockable lever 116 pivotally supported on a fulcrum pin 117 secured to the body of the clamping means 102. The opposite portion of the rockable lever 116 from the pivot pin 118 has a stepped straight portion 150 with a stop means 119. A spring 132 associated with the rockable lever 116 has an end including a roller support 136 and a roller 134 carried by the support 136, and other end pivotally anchored on a mounting member 131. With this arrangement, the spring 132 may swing about the anchored point on the mounting member 131 with the rolling of the roller 134 along the stepped portion 150 as to rockable lever 116 rocks about the fulcrum pin 117. The mounting member 131 is threadedly engaged by a threaded rod 103 whose outer end extends through a wall 102' of the body of the clamping means 102 and is provided with a spring force controlling knob at its top.

Referring again to FIG. 8, the pin 120 includes a disc 123 rigidly secured to the lower end thereof in coaxial relation with the gear 112 of the first pulley guard 111. The disc 123 (FIG. 10) has an eccentrically disposed pivot pin 125 on which a second link 124 is pivotally supported. The opposite end of the link 124 is pivotally connected through a pivot pin 128 to one end of a second rockable lever 126 pivotally supported on a second fulcrum pin 127 secured to the body of the clamping means 102. The opposite portion of the second rockable arm 126 from the pivot pin 128 has a stepped straight portion 1551 with a stop means 129. A second spring 133 associated with the second rockable lever 126 has an end including a roller support 137 and a roller carried by the support 135, and other end pivotally anchored on the mounting member 131. With this arrangement the second spring 133 swings about the anchored point on the mounting member 131 in the same manner as the first spring 132.

Referring to FIG. 9 showing an assembly of the second and third pulley guards 110 and 141, the second pulley guards rigidly supports the opposite end of the first supporting arm 101 to the end supported by the first pulley guard 111, and third pulley guard rigidly supports the second supporting arm 104 with the fourth pulley guard 160, and they are rotatably mounted through bearings 140 on a common tubular stub shaft 142 which is kept stationary by its associated pulley 146. Rotatably mounted in the sleeve 142 is a pin 142 which is rigidly connected through a dish-like fastening member 143 to the third pulley guard 141 for unitary rotation. The opposite end of the pin 142 is rigidly secured to a pulley 144 around which the ropes 145 from the pulley 146 in the first pulley guard 111 are trained.

The operation of the balance device will be presently described in reference to FIG. showing the status wherein the first supporting arm 101 positions on the line passing through the point 0 in FIG. 1. If the first supporting arm 101 is rotated about the tubular stub shaft 121 (FIG. 8) to draw an arc corresponding to the arc AB in FIG. 1, the first pulley guard 111 and the gear 112 rotate together with the first supporting arm 101. The rotation of the gear 112 drives the gear 113 in FIG. 10 in the clockwise directions, then the first link 114 pivotally connected to the pin 115 is raised up and leftwards from the position illustrated in FIG. 10, and in turn the rockable lever 116 rotates in the clockwise direction about the fulcrum pin 117. With the clockwise rotation of the rockable lever 116, the roller 134 of the spring 132 rolls towards the fulcrum pin 117 and the spring 132 is stretched in a manner that its stretch follows the characteristic of the line AB illustrated in FIG. 4 and balances the first supporting arm 101 at every position on the arc AB. If the first supporting arm 101 is rotated across the point B or through angle 90, in other words, enters in the area defined by the arc BC, the roller 134 is prevented from further rolling towards the fulcrum pin 117 by the stepped stop means 119 and is merely stretched as the rotation of the rockable lever 116 is advanced. The stretch of the spring 132 restricted at the stop means 119 follows the characteristic of line BC illustrated in FIG. 4, keeping its original spring characteristic, and balances the first supporting arm 101 at every position on the arc BC.

Next, the balance of the second supporting arm 104 will be described in reference to FIG. 9. If the second supporting arm 104 is rotated about the tubular stub shaft 142 to draw the arm AB similarly to the first supporting arm, the pin 142 rigidly fixed to the third pulley guard and the pulley 144 rigidly fixed to the pin 142 rotates together with the second supporting arm 104. The rotation of the pulley 144 is transmitted through the ropes 145 to the pulley 146, the pin 120 fixed to the pulley 146 and the disc 123 fixed to the lower end of the pin 120. If the disc 123 rotates in the counterclockwise direction (FIG. 10), the second link 124 is raised up and rightwards, to thereby rotate the second rockable lever 126 in the clockwise direction. With the clockwise rotation of the second rockable lever 126, the roller 35 of the second spring 133 rolls towards the fulcrum pin 127 and the spring 133 is stretched in a manner that its stretch follows the characteristic of the line AB illustrated in FIG. 4 and balances the second supporting arm 104 at every position on the arc AB. If the second supporting arm 104 is rotated across the point B or through angle 90, the advance of the roller 135 towards the fulcrum pin 127 is stopped by the stepped stop means 129 and is merely stretched as the rotation of the second rockable lever 126 is advanced. The stretch of the second spring 133 restricted at the stop means 119 follows the characteristic of line BC illustrated in FIG. 4, keeping its original spring characteristic, and balance the second supporting arm 104 at every position on the arc BC.

The initial spring forces of the first and second springs 132 and 133 may be controlled by turning the knob 130 so as to advance or retract the spring mounting member 131. Elongated slots 170 and 171 formed in the first and second links 114 and 124 are used to release the spring forces of the first and second springs 132 and 133 when the drafting board is turned to the horizontal level or a position close to the horizontal level. If the spring forces are not relieved, the rollers 134 and 135 move to'and-fro as the parallel motion drafting machine is moved, and impinge against their respective adjacent member and make a sound.

By providing the first and second balance devices for the parallel motion drafting machine, the first and second supporting arms 101 and 104 may be balanced independently or simultaneously at a desired position on the drafting board.

Although a preferred embodiment of the present invention has been shown and described, it will be understood that the various changes and modifications may be made in the details thereof.

What I claim is:

1. A balance mechanism for a parallel motion drafting machine having a jointed arm comprising a disk rotated by said arm, a first lever pivotally connected to said disk at an eccentric position with respect to its center, a second lever having a fulcrum for rocking motion thereof, one end of said second lever being pivotally connected to said first lever, and a spring having one end pivotally anchored and its opposite end engaged with said second lever in rolling relation therewith.

2. A balance mechanism for a parallel motion drafting machine having a support arm consisting of two support members jointedly connected comprising a disk for each support member, each disk being rotated with its corresponding suport member, a first lever for each disk, each lever pivotally being connected to its corresponding disk at an eccentric position with respect to its center, a pair of second levers each having a fulcrum for the rocking motion thereof, one end of each of said second levers being pivotally connected to said first lever, and a spring for each of said second levers, each spring having one end pivotally anchored and an opposite end engaged with said second lever in rolling relation therewith.

3. A balance mechanism in accordance with claim 1 wherein said second lever has a stop to limit the rolling of the spring.

4. A balance mechanism for a parallel motion drafting machine having a support arm consisting of two support members jointedly connected and having pulley guards at each end thereof and at the jointed connection and including a clamp and a square scale at the ends thereof comprising a gear secured to a first pulley guard to thereby transmit rotational movement of a first support member to a second gear mounted on the body of said clamp, a first link pivotally and eccentrically mounted on said second gear, a first rockable lever supported on a fulcrum pin and actuated by said first link and having a step portion, and a first spring having one end pivotally anchored and an opposite end having a roller means movable along said step portion of the rockable lever, a combined pin and pulley located in said first pulley guard and driven through the rotation of said second support member, a combined pin and pulley located at the jointed connection and rotated with and by said second support member, and ropes operatively connecting said pulleys, a disk rigidly secured to the lower end of said pin in said first pulley guard, a second link pivotally and eccentrically mounted on said disk, a second rockable lever supported on a fulcrum pin and actuated by said second link and having a step portion, and a second spring having one end pivotally anchored and an opposite end having a roller means movable along said step portion, and a spring controlling means.

References Cited UNITED STATES PATENTS 2,462,271 2/ 1949 Little et al. 2,851,779 9/1958 Cox 3379 HARRY N. HAROIAN, Primary Examiner 

